1. Field of the Invention
The invention relates to a multiple-ratio power transmission mechanism with a dual power input clutch arrangement and ratio change clutches wherein a ratio is established as an adjacent ratio is preselected during a ratio shift sequence.
2. Background Art
Automotive vehicle transmissions used, for example, in powertrains for heavy-duty or medium-duty trucks usually require a relatively high number of gear ratios in at least one range of ratios so that the speed and torque characteristics of an engine in the powertrain will provide optimal traction wheel power throughout an operating speed range. A transmission of this type is disclosed in co-pending patent application Ser. No. 11/702,359, filed Feb. 5, 2007, which is assigned to the assignee of the present invention. The transmission of the '359 patent application includes countershaft gear elements that mesh with gears mounted on a mainshaft axis. Ratio change clutches selectively connect torque transmitting gears to the mainshaft thereby establishing power delivery paths from the engine to the traction wheels. Ratio change clutches may be mounted also on a countershaft axis to selectively connect gear elements to the countershaft. It is known design practice, as in the case of the transmission disclosed in the co-pending patent application, to include a dual clutch arrangement to establish a power delivery path through the countershaft gear elements and through the mainshaft gears as one or more of the ratio change clutches are engaged. A ratio change clutch not involved in a given selected power flow path can be pre-engaged in preparation for a ratio change to an adjacent ratio. Dual clutches of the dual clutch arrangement are alternately engaged and disengaged to provide a smooth transition from one ratio to an adjacent ratio in a seamless fashion without interruption of torque delivery between the engine and the vehicle traction wheels.